From: Nikita Popov <nikita.ppv@gmail.com>
Date: Mon, 18 Mar 2019 21:35:19 +0000 (+0000)
Subject: [ValueTracking][InstSimplify] Support min/max selects in computeConstantRange()
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=348957eb04be22fbcef800639676d4ee3b0afcda;p=llvm

[ValueTracking][InstSimplify] Support min/max selects in computeConstantRange()

Add support for min/max flavor selects in computeConstantRange(),
which allows us to fold comparisons of a min/max against a constant
in InstSimplify. This was suggested by spatel as an alternative
approach to D59378. I've also added the infinite looping test from
that revision here.

Differential Revision: https://reviews.llvm.org/D59506

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@356415 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 00123788f2f..2988043c2a2 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -5680,7 +5680,28 @@ static void setLimitsForSelectPattern(const SelectInst &SI, APInt &Lower,
     return;
   }
 
-  // TODO Handle min/max flavors.
+  const APInt *C;
+  if (!match(LHS, m_APInt(C)) && !match(RHS, m_APInt(C)))
+    return;
+
+  switch (R.Flavor) {
+    case SPF_UMIN:
+      Upper = *C + 1;
+      break;
+    case SPF_UMAX:
+      Lower = *C;
+      break;
+    case SPF_SMIN:
+      Lower = APInt::getSignedMinValue(BitWidth);
+      Upper = *C + 1;
+      break;
+    case SPF_SMAX:
+      Lower = *C;
+      Upper = APInt::getSignedMaxValue(BitWidth) + 1;
+      break;
+    default:
+      break;
+  }
 }
 
 ConstantRange llvm::computeConstantRange(const Value *V, bool UseInstrInfo) {
diff --git a/test/Transforms/InstCombine/minmax-fold.ll b/test/Transforms/InstCombine/minmax-fold.ll
index d312155c523..7b66eb4a416 100644
--- a/test/Transforms/InstCombine/minmax-fold.ll
+++ b/test/Transforms/InstCombine/minmax-fold.ll
@@ -533,6 +533,37 @@ define i32 @clamp_check_for_no_infinite_loop2(i32 %i) {
   ret i32 %res
 }
 
+; Check that there is no infinite loop because of reverse cmp transformation:
+; (icmp slt smax(PositiveA, B) 2) -> (icmp eq B 1)
+define i32 @clamp_check_for_no_infinite_loop3(i32 %i) {
+; CHECK-LABEL: @clamp_check_for_no_infinite_loop3(
+; CHECK-NEXT:    [[I2:%.*]] = icmp sgt i32 [[I:%.*]], 1
+; CHECK-NEXT:    [[I3:%.*]] = select i1 [[I2]], i32 [[I]], i32 1
+; CHECK-NEXT:    br i1 true, label [[TRUELABEL:%.*]], label [[FALSELABEL:%.*]]
+; CHECK:       truelabel:
+; CHECK-NEXT:    [[I5:%.*]] = icmp slt i32 [[I3]], 2
+; CHECK-NEXT:    [[I6:%.*]] = select i1 [[I5]], i32 [[I3]], i32 2
+; CHECK-NEXT:    [[I7:%.*]] = shl nuw nsw i32 [[I6]], 2
+; CHECK-NEXT:    ret i32 [[I7]]
+; CHECK:       falselabel:
+; CHECK-NEXT:    ret i32 0
+;
+
+  %i2 = icmp sgt i32 %i, 1
+  %i3 = select i1 %i2, i32 %i, i32 1
+  %i4 = icmp sgt i32 %i3, 0
+  br i1 %i4, label %truelabel, label %falselabel
+
+truelabel: ; %i<=1, %i3>0
+  %i5 = icmp slt i32 %i3, 2
+  %i6 = select i1 %i5, i32 %i3, i32 2
+  %i7 = shl nuw nsw i32 %i6, 2
+  ret i32 %i7
+
+falselabel:
+  ret i32 0
+}
+
 ; The next 3 min tests should canonicalize to the same form...and not infinite loop.
 
 define double @PR31751_umin1(i32 %x) {
diff --git a/test/Transforms/InstSimplify/cmp_of_min_max.ll b/test/Transforms/InstSimplify/cmp_of_min_max.ll
index 4726609c3f5..34c4a15aed1 100644
--- a/test/Transforms/InstSimplify/cmp_of_min_max.ll
+++ b/test/Transforms/InstSimplify/cmp_of_min_max.ll
@@ -3,10 +3,7 @@
 
 define i1 @test_umax1(i32 %n) {
 ; CHECK-LABEL: @test_umax1(
-; CHECK-NEXT:    [[C1:%.*]] = icmp ugt i32 [[N:%.*]], 10
-; CHECK-NEXT:    [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 10
-; CHECK-NEXT:    [[C2:%.*]] = icmp ugt i32 [[S]], 9
-; CHECK-NEXT:    ret i1 [[C2]]
+; CHECK-NEXT:    ret i1 true
 ;
   %c1 = icmp ugt i32 %n, 10
   %s = select i1 %c1, i32 %n, i32 10
@@ -40,10 +37,7 @@ define i1 @test_umax3(i32 %n) {
 
 define i1 @test_umin1(i32 %n) {
 ; CHECK-LABEL: @test_umin1(
-; CHECK-NEXT:    [[C1:%.*]] = icmp ult i32 [[N:%.*]], 10
-; CHECK-NEXT:    [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 10
-; CHECK-NEXT:    [[C2:%.*]] = icmp ult i32 [[S]], 11
-; CHECK-NEXT:    ret i1 [[C2]]
+; CHECK-NEXT:    ret i1 true
 ;
   %c1 = icmp ult i32 %n, 10
   %s = select i1 %c1, i32 %n, i32 10
@@ -77,10 +71,7 @@ define i1 @test_umin3(i32 %n) {
 
 define i1 @test_smax1(i32 %n) {
 ; CHECK-LABEL: @test_smax1(
-; CHECK-NEXT:    [[C1:%.*]] = icmp sgt i32 [[N:%.*]], -10
-; CHECK-NEXT:    [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 -10
-; CHECK-NEXT:    [[C2:%.*]] = icmp sgt i32 [[S]], -11
-; CHECK-NEXT:    ret i1 [[C2]]
+; CHECK-NEXT:    ret i1 true
 ;
   %c1 = icmp sgt i32 %n, -10
   %s = select i1 %c1, i32 %n, i32 -10
@@ -114,10 +105,7 @@ define i1 @test_smax3(i32 %n) {
 
 define i1 @test_smin1(i32 %n) {
 ; CHECK-LABEL: @test_smin1(
-; CHECK-NEXT:    [[C1:%.*]] = icmp slt i32 [[N:%.*]], 10
-; CHECK-NEXT:    [[S:%.*]] = select i1 [[C1]], i32 [[N]], i32 10
-; CHECK-NEXT:    [[C2:%.*]] = icmp slt i32 [[S]], 11
-; CHECK-NEXT:    ret i1 [[C2]]
+; CHECK-NEXT:    ret i1 true
 ;
   %c1 = icmp slt i32 %n, 10
   %s = select i1 %c1, i32 %n, i32 10